2026-09-29 / Signal #3
ChatGPT, Claude, Gemini and Grok are leaking chat contents to advertisers
“Your most private prompt is now an ad-targeting string.”
The Story
Spanish researchers found that major chatbot web apps—including ChatGPT, Gemini, Claude, Grok, Perplexity, and Mistral—send conversation artifacts to advertising and analytics networks. That can include chat titles, questions, uploaded documents, and even screenshots; Grok was the worst case, with conversations public by default and URLs hitting Meta, TikTok, Google Ads, and X analytics. Spain’s data-protection agency has referred the findings toward European-level review.
Why It Matters
You told the machine you might have Parkinson. The machine titled the chat. The title went to an ad exchange. Confession as inventory.
Evidence
elDiario.es (IMDEA Networks / Universidad Carlos III de Madrid); HN PDF “Prompt like a butterfly, sting like a tracker
Sources
Daily scan: 2026-09-29